Polymerization of propylene is commercially useful, therefore there is a need in the art for more efficient propylene polymerization processes. State-of-the-art commercial processes polymerize propylene in particle-forming processes, known in the art as gas phase and slurry polymerization. These processes are very efficient for making polypropylenes, but they are unable to produce blends of polypropylene and other polymers in-line, i.e., before the individual polymer blend components are recovered in their essentially neat state. For that reason, state-of-the-art processes for producing polyolefin blends, particularly blends of polypropylene with other polymers, such as, for example, ethylene-propylene, or ethylene-hexene-1, etc., copolymers, blend fully-recovered, typically granulated polypropylene with other fully-recovered, typically granulated polyolefin blend components via melt-blending. However, melt-blending is expensive and not perfectly homogeneous, due to the difficulty of blending the highly viscous molten polymers. Solution polymerization would be able to make the polypropylene component in a dissolved fluid state, suitable for blending with other polymers also produced in a dissolved state. However, the molecular weight and the thermal properties of polypropylene made in a solution process are often unacceptable for producing commercially useful polymer blends. Thus, there is a need for an improved solution process for the production propylene-containing polymers, particularly, polypropylenes, to enable solution operations amenable for in-line polymer blending without unacceptable deterioration in the performance of the polypropylene blend component. The disclosed supersolution processes overcome these limitations of the current state of the art and are able to produce polypropylenes that combine excellent (low) melt-flow rate and high melting and crystallization temperatures. There are several processes disclosed that operate in homogeneous state amenable for in-line polymer blending in solution. However, they are either deficient in product quality or are too expensive and thus commercially not practical.
U.S. Pat. No. 6,084,041, granted to Andtsjo et al., discloses supercritical propylene polymerization under relatively mild conditions (90° C. to 100° C. and less than 6.89 MPa pressure) using supported Ziegler-Natta and metallocene catalysts.
WO 93/11171 discloses a polyolefin production process that comprises continuously feeding olefin monomer and a metallocene catalyst system into a reactor. The monomer is continuously polymerized to provide a monomer-polymer mixture. Reaction conditions keep this mixture at a pressure below the system's cloud-point pressure. These conditions create a polymer-rich and a monomer-rich phase and maintain the mixture's temperature above the polymer's melting point. The formation of the viscous polymer-rich phase tends to make reactor and downstream operations problematic due to fouling, unintended bulk phase separation, and poor heat transfer.
WO 03/040201 discloses polymerization or propylene with nonmetallocene metal-centered, heteroaryl ligand catalyst compounds under non-supersolution conditions.
Other references of interest include: Olefin Polymerization Using Highly Congested ansa-Metallocenes under High Pressure: Formation of Superhigh Molecular Weight Polyolefins, Suzuki, et al., Macromolecules, 2000, 33, 754-759, EP 1 123 226, WO 00 12572, WO 00 37514, EP 1 195 391, and Ethylene Bis(Indenyl) Zirconocenes . . . , Schaverien, C. J. et al., Organometallics, ACS, Columbus Ohio, vol 20, no. 16, August 2001, pg 3436-3452, WO 96/34023, WO 97/11098, U.S. Pat. No. 5,084,534, U.S. Pat. No. 2,852,501, WO 93/05082, EP 129 368 B1, WO 97/45434, JP 96-208535, U.S. Pat. No. 5,096,867, WO 96/12744, U.S. Pat. No. 6,225,432, WO 02/090399, WO 02/50145, US 2002 013440, WO 01/46273, EP 1 008 607, JP-1998-110003A, U.S. Pat. No. 6,562,914, and JP-1998-341202B2, U.S. Pat. No. 5,756,608, U.S. Pat. No. 5,969,062 U.S. Pat. No. 5,408,017, U.S. Pat. No. 6,355,741, WO 92/14766, U.S. Pat. No. 5,326,835, WO/2004-026921 and CA 2,118,711 (equivalent to DE 4,130,299).
WO 02/38628 describes nonmetallocene, metal-centered, heteroaryl ligand catalyst compounds and various uses therefor. WO2006/009976 discloses polymerizations in fluorocarbons with various nonmetallocene, metal-centered, heteroaryl ligand catalyst compounds. Further, WO03/040095, WO 03/040202; WO 03/040233; WO 03/040442; and U.S. Pat. No. 7,087,690, describe nonmetallocene, metal-centered, heteroaryl ligand catalyst compounds, their polymer products, and various uses therefor.
WO 94/00500, WO 2007/037944 and Macromol. Chem. Phys. 204 (2003), 1323-1337 disclose various solution processes to make polypropylene.